 Moving on, let's discuss warfarin. Warfarin inhibits epoxide reductase, which is going to interfere with our gamma carboxylation of vitamin K dependent clotting factors. Those specific clotting factors it works against are 2, 7, 9, 10, protein C and protein S. This picture does exclude the intrinsic pathway, which will affect 2 and 9, as far as our coagulation cascade goes. But it does have a effect on 7, 10, protein C and protein S. What do we use warfarin for? Chronic anticoagulation. If a patient has an indication that shows that they need to be on anticoagulation for a long period of time due to hypercoagulability, then we will use warfarin as one of the most common medications to anticoagulate. A negative thing that we do have with warfarin is it does require us to check labs. So we need to check our PT and INR weekly to be sure that we are within a therapeutic range and not over anticoagulating or under anticoagulating. Side effects associated with warfarin include bleeding, as we would expect for an anticoagulant. It is very tratogenic, so that means it's contraindicated in patients that are or expect to become pregnant. We can also see a problem called skin or tissue necrosis. So warfarin can actually cause a micro thrombosis in the skin layers and the dermal layers that can present as what appears to be a very nasty dark colored bruise. You can see here in this picture on the lower extremity of this patient. This typically shows up in the first few days of a very large dose. We can also see some drug to drug interactions with warfarin. One of the benefits that warfarin has over some of our other anticoagulants is that it can be very easily reversed. So we can give vitamin K because this does affect our vitamin K dependent clotting factors. So giving vitamin K will help increase those vitamin K dependent clotting factors. Or in a very acute situation we can give fresh frozen plasma. It is noteworthy that warfarin does take a small amount of time for it to become therapeutic within a patient. Therefore we will do something called heparin bridge where we began a patient on warfarin and heparin at the same time. And then a few days later once we know that our warfarin is at a therapeutic level because we've been checking their PT and INR. Then we can discontinue the heparin and continue on with the warfarin at our therapeutic levels. This basically helps reduce the risk of a recurrent venous thromboembolism. And it does also help reduce the risk of skin and tissue necrosis associated with warfarin.